1. Field of the Invention
The present invention relates to a method of separating a particular component from the liquid solution thereof through the use of a permeable membrane, and more particularly to such a method of separating the component in vapor-to-vapor phase permeation, which might be termed as an "evapomeation" method as coined from the words "evaporation" and "permeation" for well describing the novel liquid separation method of the present invention.
2. Description of the Prior Art
As a method of separating a particular component from its liquid solution or mixture such as an organic liquid containing two or more kinds of components there has been so far employed a distillation. But the distillation requires a great deal of energy input for heating the liquid solution. Hence, a reverse osmosis method is utilized as one of membrane separation methods for separating of the liquid solution. But in the reverse osmosis method, since it is required to pressurize the liquid solution under a high pressure in order that a particular component intended to be separated can permeate effectively through a permeable membrane from a more concentrated solution side to a less concentrated solution side, the permeable membrane will be readily densified by such pressurization to lower its permeation efficiency, whereby its separating performance will be considerably limited.
In this consequence, a study has been directed to a pervaporation (permeation evaporation) method which is also the membrane separation method but requires no pressurization, as shown for example in the U.S. Pat. No. 4,218,312. The principle of this pervaporation method will be briefly discussed with reference to FIG. 3 in which an apparatus for the method is schematically shown to have a separation vessel 25 divided into an upper solution chamber 23 and a lower vacuum chamber 21 by means of a permeable membrane 24. By reducing a pressure in the vacuum chamber 21 while keeping the solutions 22 introduced into the solution chamber 23 in contact with the membrane 24, a particular component in the liquid solution 22 will permeate and diffuse through the permeable membrane 24 selectively in preference to the other components so that the component having permeated can evaporate from the surface of the permeable membrane 24 into the vacuum chamber 21. With this method, it is possible to effect the separation of the liquid solution by recovering the particular component thus permeated through the membrane 24 and evaporated into the vacuum chamber 21 or alternatively by recovering the remaining solution in the solution chamber 23.
As explained in the above, the pervaporation method enables to separate the liquid solution through a permeable membrane without requiring any pressurization as in the reverse osmosis method and also without causing the membrane to be undesirably densified.
However, in the above pervaporation method in which the liquid solution is kept in direct contact with the permeable membrane, there arises another problem that the permeable membrane which is generally made from a macromolecular material is likely to be swelled due to the direct contact with the solution. When the permeable membrane is swelled, its permeability will be degraded to thereby lower the separation efficiency.